Why Diets Make Us Fat

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  • Could our ceaseless preoccupation with weight loss actually be making us fatter? Four years after losing weight, 40% of dieters are heavier than they were originally. Neuroscientist Sandra Aamodt, author of new book, ‘Why Diets Make Us Fat‘, set out to find out why – and what we can do about it…

    According to Sandra, each of us has a set ‘brain weight’, zealously defended by a ‘thermostat’ in our brains. This control centre not only moderates metabolism, but directs our urges to eat and get physical. “Left to its own devices, the energy balance system can maintain a stable weight for most people more effectively than deliberate attempts to calculate our calorie needs and intake,” says Aamodt. In theory, if you eat when you’re hungry, stop when you’re full and exercise daily (a long walk or dance class counts), you’re laughing.

    So what’s the problem? Well, it’s twofold. Firstly, years of yo-yo dieting have caused us to lose the ability to recognise our body’s signals of hunger and fullness, making us more vulnerable to emotional eating and prone to developing unhealthy habits.

    The stress exerted on the body by dieting encourages the release of cortisol, which, in turn, stimulates the release of ghrelin (the ‘hunger hormone’), buffers the effects of leptin (the hormone which signals to our brains that we are full) and causes the brain to register the experience of eating as more rewarding. The persistent over-production of cortisol also promotes the laying down of visceral fat around the abdomen.

    Meanwhile, the brain responds to ‘starvation’ by triggering urges to binge eat and reducing the rate at which calories are burned. Those who have previously suffered severe involuntary deprivation are at an increased risk of being classed as obese several years down the line. Extreme dieting could well have similar effects…

    Secondly, your ‘brain weight’ may have settled at a higher level than you’d like. Thank human evolution, which has endowed us with weak protection against weight gain and strong protection against weight loss. It’s relatively easy to maintain a bodyweight within about a stone of our ‘brain weight’, but it is far easier to settle at a ‘new normal’ level having gained a substantial amount of weight than having lost it.

    People whose body weight is 10% lower than the range ‘defended’ by their brain’s regulatory system burn 10-15% fewer calories than those whose weight lies within their defended range, even if their weights are the same. No, it’s not fair. And, unfortunately, it might mean that maintaining your ‘goal’ weight long-term would necessitate a lifetime of constant hunger. No wonder you’re tempted to throw in the towel in favour of a Krispy Kreme – or twelve.

    Throwing a further spanner in the works, research has found that people were heavier in 2006 than those reporting identical eating and exercise habits 18 years earlier. Yes, modern life is conspiring to make us fat – even chimps and wild rats have ballooned in size. Exposure to pesticides and plastics can cause genetic changes which promote obesity and can be inherited by successive generations, which Aamodt believes may affect ‘brain weight’.

    What can you do about it?

    Our ‘brain weight’ is determined by a combination of genetic factors and lifestyle experience. If a lifetime of yo-yo dieting, lack of exercise and unhealthy habits has conspired to turn up the dial on yours, though, it’s not necessarily too late to act.

    Eat intuitively

    Eat when you’re hungry, stop when you’re full and stop counting calories. Aamodt tracked her diet over a year of ‘non-dieting’ and found that her calorie intake naturally varied from 1,400 to 2,400, averaging out at 1,800. “My brain, it seems, was much better at keeping track of my calorie intake than my dieting regimes had ever been,” she says.

    Eat mindfully

    In order to eat intuitively, you first need to train yourself to recognise those all-important signals of hunger and fullness. Try to eat when you are moderately hungry, rather than ravenous, and take your time, as it can take up to 20 minutes for the signal that you are full to reach your brain. For more tips on mindful eating, read our feature on how to train your brain to eat less.

    Reduce stress

    Reduce the devastating effects of stress hormones on your appetite by practising mindfulness more generally. Getting sufficient sleep is also important – those who don’t get enough release more cortisol.

    Eat real food

    Your brain’s energy balance system can deal much more accurately with ‘real food’, so cook from scratch whenever possible, replacing processed foods with vegetables, whole grains and natural sources of protein and essential fatty acids where you can. It’s particularly important to consume as many foods with anti-inflammatory benefits as possible – cellular inflammation may cause your brain to become resistant to leptin (the hormone which tells your brain that you are full).


    Exercise doesn’t just burn calories – it also reduces inflammation, and too little can put your brain’s energy-balance system out of whack. Office workers eat more than those whose jobs involve even minimal amounts of movement – so book your place at that lunchtime yoga class.

    Build healthy habits

    Make exercising, eating well and being mindful part of your daily life. Aamodt advises trying to replace unhealthy habits with healthy ones (e.g. eating an apple after lunch, rather than a chocolate bar, or walking to the train station rather than catching a bus) and kick-starting lifestyle changes during times of low stress (e.g. on holiday). It can take up to 9 months for a habit change to ‘stick’ so be patient with yourself. It’s important to perform each action in the same context each day. If you can, follow it up with a reward, e.g. a hot bath or a phone call to a friend.

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